-LRB- CNN -RRB- -- A gunman killed three people and wounded at least five at the house of a mayoral candidate in the Philippines before polls opened on Monday , a military spokeswoman said .

The attack happened around 2:30 a.m. -LRB- 2:30 p.m. Sunday ET -RRB- when an unidentified gunman raided the house of a mayoral candidate in Zamboanga del Sur province , said spokeswoman Steffani Cacho . The incident is under investigation , she added .

More than 50 million ballots have been printed with a dizzying number of candidates to choose from -- nine for president alone , among them front-runner Sen. Benigno Aquino III , son of a former president ; and Joseph Estrada , a former president himself .

Family dynasties also play a role : Former first lady Imelda Marcos is running to fill the Congressional seat of her son , Ferdinand `` Bongbong , '' who is running for Senate , while her Congresswoman daughter Imee is running for governor .

Boxing champion Manny Pacquiao also threw his hat in the ring : He 's running for Congress too .

In all . voters must fill some 17,000 other positions at the executive , legislative and local levels .

A faulty test run of automated machines raised questions as late as Wednesday of whether the elections would even happen . A postponement would have stirred fears of a power vacuum on June 30 when President Gloria Macapagal-Arroyo is scheduled to end her nine years in office .

Polls opened to crowds of waiting voters , CNN 's Arwa Damon reported from Manila .

`` People are very excited , '' Damon said , adding that the election-day mood was `` tinged with anxiety . ''

Polls were scheduled to remain open until 6 p.m. local time -LRB- 10 a.m. GMT -RRB- .

`` It 's a very crucial litmus test to our democracy , our fragile democracy , '' said Leila De Lima , chairwoman of the Commission on Human Rights of the Philippines , which will be serving as an independent election monitor . `` The administration has been hounded by issues of corruption , human rights violations . People are looking forward to a new administration that will hopefully usher in meaningful changes . So , it 's very , very important . ''

`` The right of suffrage is a fundamental human right , '' she added .

The Philippine National Police -LRB- PNP -RRB- has been placed on nationwide full alert since last week , with all leaves canceled , and all 130,000 officers required to report for duty .

An election ban on liquor sales and public consumption went into effect Sunday , with violators subject to one to six years in prison . Exemptions are made for hotels and tourist-oriented establishments with prior approval . A nationwide gun ban has already been in force since January 10 at the start of the election period .

Vote buying is `` currently the most common form of cheating , '' the PNP quoted its chief and director-general Jesus Verzosa as saying .

Whereas in the past , people were paid to vote , this time they are paid to waive their right to vote and have their index fingers marked with ink , making them ineligible , according to PNP . Reports indicated some candidates were willing to pay identified supporters of their opponents not to vote , the PNP said on its Web site .

The proliferation of guns and private armies , particularly those attached to political families , has contributed to a violent atmosphere , particularly in the country 's southern province of Maguindanao , where 57 people were massacred in November .

The transparency of the election process also has also been called into question . Election watchdog group Kontra Daya on Saturday condemned the Commission on Elections ' approval of presidential son Juan Miguel Arroyo as first nominee of a political party made up entirely of security guards . The party is running as one of 187 `` party-list groups '' that are designated as marginalized and underrepresented and would together comprise one-fifth of the House of Representatives .

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Last month Kontra Daya identified 40 questionable party-list groups , showing their links to various people in the Arroyo administration or the president 's family , including her sister-in-law , who represents a party of small entrepreneurs .

Not to be outdone is the inclusion on millions of ballots of a person whose name may appear at the top of the list of presidential candidates -- and above Aquino 's -- despite being disqualified in March : Vetellano Acosta .

The Commission on Elections said Acosta , who is listed under the `` KBL '' party founded by Ferdinand Marcos , would remain on the ballot because so many ballots had already been printed .

CNN 's Elizabeth Yuan contributed to this report .

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NEW : Killing of three people at mayoral candidate 's house under investigation

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Polls open and will close at 6 p.m. local time

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Voters choose a new president , vice president and 17,000 other positions

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Philippine National Police -LRB- PNP -RRB- on nationwide full alert since last week